1. Field of the Invention
The present invention relates to a linear drive, a control device for a convertor, a computer program and a control method for a primary part of the linear drive.
2. Description of the Related Art
Various embodiments of control methods for linear drives are known. For example, “regulated operation” is particularly known. In regulated operation, the segments of a primary part of the linear drive receive a quadrature-axis component of current which is precisely sufficient to cause a movement of a respective carrier in a respective segment of the primary part. Here, the carrier has a number of secondary parts that are statically arranged within the respective carrier. Regulated operation is a prerequisite for DE 101 50 318 A1 and DE 101 50 319 C1, for example. Regulated operation is also a prerequisite for DE 10 008 602 A1. In particular, DE 10 008 602 A1 explains how a carrier can be transferred from segment to segment of the primary part in a simple manner.
An important aspect of regulated operation is that only one single carrier is ever allowed to be present in each segment of the primary part. Using regulated operation, it is therefore impossible to move more than one carrier within the same segment of the primary part. This also applies when transferring a carrier from one segment of the primary part to the next segment of the primary part. Here, neither of the segments concerned is allowed to contain another carrier.
Depending on the application, the restriction that only one single carrier is allowed to be present in a segment of the primary part may be a significant disadvantage. In applications for the packaging industry or in manufacturing equipment (e.g. machine tools), for example, efficiency could be significantly increased if it were possible to move trains, i.e., a sequence of closely following carriers.
So-called “controlled operation” for linear drives is also known. In the context of controlled operation, the segments receive a direct-axis component of current which is so dimensioned as to be sufficient to reliably cause the movement of the carrier that is situated in the respective segment. The quadrature-axis component of current is kept as small as possible, or is pre-controlled by specifying a corresponding desired value for the quadrature-axis component of current. By advancing the direct-axis component of current in accordance with the desired movement, the carriers follow the magnetic field produced by the direct-axis component of current in a similar way to the movement of the rotor of a synchronous machine. This operating mode allows a plurality of carriers to be moved simultaneously in each segment of the primary part. Therefore, a plurality of carriers may be present simultaneously in the respective segment of the primary part. In the context of controlled operation, often also referred to as “I/f operation” in practice, the carriers can however experience mechanical vibrations which are superimposed on the desired movement of the carriers. Damping of such vibrations is required in many cases. Possibilities for damping such vibrations are known per se. Reference is made to DE 195 19 238 A1 by way of example only. However, only insufficient damping of vibrations that occur when transferring a carrier from one segment to another segment is possible using conventional methods.